Showing papers on "Claisen rearrangement published in 2017"
TL;DR: Mechanistically, C-glycosylation reactions can involve glycosyl electrophilic/cationic species, anionic species, radical species, or transition-metal complexes, which are discussed as subcategories under each type of sugar precursor.
Abstract: Advances in the chemical synthesis of C-pyranosides/furanosides are summarized, covering the literature from 2000 to 2016. The majority of the methods take advantage of the construction of the glycosidic C—C bond. These C-glycosylation methods are categorized herein in terms of the glycosyl donor precursors, which are commonly used in O-glycoside synthesis and are easily accessible to nonspecialists. They include glycosyl halides, glycals, sugar acetates, sugar lactols, sugar lactones, 1,2-anhydro sugars, thioglycosides/sulfoxides/sulfones, selenoglycosides/telluroglycosides, methyl glycosides, and glycosyl imidates/phosphates. Mechanistically, C-glycosylation reactions can involve glycosyl electrophilic/cationic species, anionic species, radical species, or transition-metal complexes, which are discussed as subcategories under each type of sugar precursor. Moreover, intramolecular rearrangements, such as the Claisen rearrangement, Ramberg–Backlund rearrangement, and 1,2-Wittig rearrangement, which usuall...
314 citations
TL;DR: An efficient yttrium-catalyzed intramolecular hydroalkoxylation/Claisen rearrangement sequence has been achieved, thus enabling facile access to a diverse array of valuable medium-sized lactams.
Abstract: An efficient yttrium-catalyzed intramolecular hydroalkoxylation/Claisen rearrangement sequence has been achieved, thus enabling facile access to a diverse array of valuable medium-sized lactams. Furthermore, a mechanistic rationale for this novel cascade reaction is well supported by a variety of control experiments.
118 citations
TL;DR: In this article, a variety of simple strategies demonstrated in our laboratory in the last two decades for the assembly of diverse and intricate molecular frameworks containing spiro linkage(s) by using various metathesis protocols such as ring-closing metatheses (RCM), ring-opening cross-metathesis (ROCM) and ring-rearrangement metatheses (RRM).
76 citations
TL;DR: A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized and a range of acyclic α-allyl β-keto esters were synthesized in high yields with good diastereoselectivities and excellent enantioselectivity under mild reaction conditions.
Abstract: A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π-acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N′-dioxide–nickel(II) complex. A range of acyclic α-allyl β-keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee) under mild reaction conditions. These products can be easily transformed into optically active β-hydroxy esters, β-hydroxy acids, or 1,3-diols.
75 citations
TL;DR: In this article, the synthesis and pharmacological evaluation of new series of 4-((3-aryl-4,5-dihydroisoxazol-5-yl)methoxy)-2H-chromen-2-ones 3a-f prepared by cycloaddition reaction using various arylnitrile oxides with the suitable 4-(allyloxy)2H-(chromen)-2-one 2a 2a is described.
38 citations
TL;DR: This protocol provides a facile entry to 2,2-disubstituted indolin-3-ones, which have been applied in the construction of the benzofuroindoline framework related to Phalarine.
29 citations
TL;DR: In this paper, a rhodium-catalyzed intramolecular tandem reaction of vinyloxirane-alkynes leading to four structurally distinct classes of mono-, bi-, and tricyclic carbocycles and heterocycles was developed.
Abstract: Skeletal diversity in diversity-oriented synthesis has proven to be especially challenging. A rhodium-catalyzed intramolecular tandem reaction of vinyloxirane-alkynes leading to four structurally distinct classes of mono-, bi-, and tricyclic carbocycles and heterocycles was developed. [Rh(NBD)2]+BF4– is identified to be an efficient catalyst for these transformations. Using this highly efficient catalyst, hetero-[5 + 2] cycloadditions, tandem hetero-[5 + 2] cycloaddition/Claisen rearrangements, and subsequent cyclopropane ring-opening reactions of vinyloxiranes with monoalkynes afford 2,5-dihydrooxepins, tetrasubstituted vinylcyclopropanes, and multifunctional five-membered rings, respectively, under mild conditions with high stereoselectivity and yield. Moreover, hetero-[5 + 2] cycloaddition/Claisen rearrangement/[5 + 2] cycloaddition reactions of vinyloxiranes with diynes for step-economical construction of linearly fused 5-7-5 tricyclic skeletons has also been developed. The complete transfer of chiral...
27 citations
TL;DR: The first total synthesis of the hexacyclic indole alkaloid (±)-corymine is described, starting from the readily available N-protected tryptamine and achieved in 21 steps in 3.4 % overall yield.
Abstract: The first total synthesis of the hexacyclic indole alkaloid (±)-corymine is described. Starting from the readily available N-protected tryptamine, the title compound was achieved in 21 steps in 3.4 % overall yield. Key steps of the synthesis include: a) the addition of a malonate to a 3-bromooxindole to afford 3,3-disubstituted oxindole, b) the formation of a 12-membered cyclic enol ether by intramolecular O-propargylation, immediately followed by propargyl Claisen rearrangement to provide the α-allenyl ketone stereospecifically, c) DMDO oxidation to install a hydroxy group in a highly stereoselective manner, and d) the SmI2-mediated reductive C−O bond cleavage to remove the α-keto carboxyl group.
26 citations
TL;DR: A new approach has been developed for the synthesis of 8-substituted 2H-chromenes, featuring a novel cascade aromatic Claisen rearrangement/o-quinone methide formation/6π-electrocyclization.
26 citations
TL;DR: A one-pot microwave-assisted method for the synthesis of cinnamic acid and coumarin derivatives that provides high product yields and selectivities without the need of a phenol protecting group is described.
25 citations
TL;DR: A novel functionality was introduced in the pillararene family by the Claisen rearrangement of monoallyl pillar[5]arene that can lead to the formation of a 10 + 1 functionalized derivative, a useful scaffold for further derivatization.
TL;DR: A facile, diastereoselective synthesis of highly substituted pyrrolidine-2,3-diones is reported, along with the one-step conversion of these heterocycles to novel β-amino acids and further functionalized derivatives.
TL;DR: In this article, a thermally induced Claisen rearrangement of bis-allyl ether-substituted deoxybenzoin (BA-BHDB) was proposed.
Abstract: We describe the synthesis of allyl-substituted deoxybenzoin-based aromatic polyesters that combine the advantageous thermal properties of deoxybenzoin with the processability and reactivity of pendent unsaturated groups. A thermally induced Claisen rearrangement of bis-allyl ether-substituted deoxybenzoin 2 produced 3,3′-bis-allyl-4,4′-bishydroxydeoxybenzoin (BA-BHDB, compound 1) as a novel A2 monomer. BA-BHDB 1 polymerized readily with isophthaloyl chloride to produce a novel set of functional aromatic polyesters. These allyl-substituted polymers exhibited marked solubility advantages over deoxybenzoin-based polymers lacking such pendent groups, affording homogeneous solutions in numerous organic solvents. The processability contributed by the allyl groups afforded access to relatively high molecular weight aromatic polyesters, with estimated number-average molecular weight (Mn) values exceeding 20 kDa. Interestingly, evaluation of the thermal properties of these polymers revealed that the pendent allyl ...
TL;DR: Recent advances in aza-Claisen-rearrangement-induced ring-expansion strategy are summarized, in particular applications in the synthesis of bioactive alkaloids.
TL;DR: In this article, a variety of structurally interesting oxygenated cage compounds involving atom-economic processes such as Claisen rearrangement, Diels-Alder reaction, [2+2] photocycloaddition, and ring-closing metathesis (RCM) are reported.
Abstract: The preparation of a variety of structurally interesting oxygenated cage compounds involving atom-economic processes such as Claisen rearrangement, Diels–Alder reaction, [2+2] photocycloaddition, and ring-closing metathesis (RCM) as key steps is reported. For the first time, oxepane ring system is introduced in cage framework using olefin metathesis as a key step. These cage systems assembled here are difficult to prepare by traditional methods. The synthetic sequence described here opens up new routes to higher order polycycles containing heteroatoms without the involvement of protecting groups. Transannular cyclization observed during Grignard addition and the RCM protocol used here may be applicable to generate unknown oxygenated cage systems.
TL;DR: Claisen rearrangements of allyl aryl ethers to generate enones bearing all carbon quaternary centers are accelerated by Ph3PAuNTf2 under mild conditions in good yields.
TL;DR: This work developed a concise synthetic route for the synthesis of polysubstituted naphthalenes starting from commercially available isovanillin and its derivatives through reaction with styryl bromide.
Abstract: In this work, we developed a concise synthetic route for the synthesis of polysubstituted naphthalenes starting from commercially available isovanillin and its derivatives. Reaction with styryl bromide via O-styrylation, Claisen rearrangement, ene reaction, and O-alkylation occurred in high yields. The key structures were confirmed by single-crystal X-ray diffraction.
TL;DR: Mechanistic studies confirm that 1-propenylnaphthols are the key intermediates to form the 3-arylnaphtho[2,1-b]furans and these two operationally simple and practical protocols could be scaled up to a gram level.
Abstract: A simple and efficient strategy for the synthesis of 1-propenylnaphthols from readily accessible 3-arylallylnaphthyl ethers has been developed. By using K2CO3 as base and 2-methoxyethanol as solvent, direct access to a wide range of 1-propenylnaphthols can be achieved in generally good yield (up to 99%) with high stereoselectivity toward the Z isomer. The control experiments indicate that the reaction proceeds through a sequential Claisen rearrangement/isomerization process. Furthermore, starting from the same material, the highly valuable 3-arylnaphtho[2,1-b]furans can be obtained in N,N-dimethylformamide and in the presence of Ag2O as the oxidant via a one-pot sequential Claisen rearrangement/isomerization/cyclization reaction. Mechanistic studies confirm that 1-propenylnaphthols are the key intermediates to form the 3-arylnaphtho[2,1-b]furans. In addition, these two operationally simple and practical protocols could be scaled up to a gram level.
TL;DR: An efficient yttrium-catalyzed tandem intermolecular hydroalkoxylation/Claisen rearrangement has been developed, providing various γ,δ-unsaturated amides in generally good to excellent yields.
Abstract: An efficient yttrium-catalyzed tandem intermolecular hydroalkoxylation/Claisen rearrangement has been developed, providing various γ,δ-unsaturated amides in generally good to excellent yields. Importantly, high Z/E selectivity and diastereoselectivity were achieved. Other notable features of this method include widespread availability of the substrates, compatibility with a broad range of functional groups, and mild reaction conditions.
TL;DR: The Ireland-Claisen rearrangement sequence applied to readily available propargyl glycolates was developed as a route toward functionalized alkylidene incorporating a quaternary stereocenter and a protected glycolic acid moiety, which are useful building blocks for the preparation of functionalized gem-difluorocyclopropanes.
Abstract: A one-pot difluorocyclopropenation/Ireland–Claisen rearrangement sequence applied to readily available propargyl glycolates was developed as a route toward functionalized alkylidene(gem-difluorocyclopropanes). This strategy conveniently avoids the isolation of the unstable 3,3-difluorocyclopropenylcarbinyl glycolates arising from the difluorocyclopropenation. The Ireland–Claisen rearrangement proceeds with high diastereoselectivity and chirality transfer to afford alkylidene(gem-difluorocyclopropanes) incorporating a quaternary stereocenter and a protected glycolic acid moiety, which are useful building blocks for the preparation of functionalized gem-difluorocyclopropanes.
TL;DR: It is demonstrated that the reaction mechanisms can be complicated in homogeneous solutions since the solvent–solute interactions can profoundly influence the reaction dynamics and the energy transfer process.
Abstract: Efficient sampling in both configuration and trajectory spaces, combined with mechanism analyses via data mining, allows a systematic investigation of the thermodynamics, kinetics, and molecular-detailed dynamics of chemical reactions in solution. Through a Bayesian learning algorithm, the reaction coordinate(s) of a (retro-)Claisen rearrangement in bulk water was variationally optimized. The bond formation/breakage was found to couple with intramolecular charge separation and dipole change, and significant dynamic solvent effects manifest, leading to the “in-water” acceleration of Claisen rearrangement. In addition, the vibrational modes of the reactant and the solvation states are significantly coupled to the reaction dynamics, leading to heterogeneous and oscillatory reaction paths. The calculated reaction rate is well interpreted by the Kramers’ theory with a diffusion term accounting for solvent–solute interactions. These findings demonstrated that the reaction mechanisms can be complicated in homoge...
TL;DR: The synthesis of the briarane-brianthein A core has been accomplished utilizing an extension of the dianionic Ireland-Claisen rearrangement to establish the C1 quaternary carbon and the adjacent C10 ring juncture stereocenters.
TL;DR: Analysis of the solvent effects on the Cope rearrangement of 3-phenyl-1,5-hexadiene indicated that a solvophobic effect was responsible for the observed rate enhancement in the ionic liquid, and that this was due to preferential solvation of the transition state.
Abstract: Simple Cope and Claisen rearrangements were investigated in an ionic liquid and a range of molecular solvents through a series of kinetic studies. Analysis of the solvent effects on the Cope rearrangement of 3-phenyl-1,5-hexadiene indicated that a solvophobic effect was responsible for the observed rate enhancement in the ionic liquid, and that this was due to preferential solvation of the transition state. A similar solvophobic effect contributes to the ionic liquid solvent effect on the Claisen rearrangement of allyl vinyl ether, although the ability of the ionic liquid to stabilise the incipient charges in the transition state also likely contributes to the rate increase observed in the ionic liquid solvent. The activation parameter data suggest that in this case the ionic liquid was interacting with species along the reaction coordinate through general coulombic interactions (more acetonitrile-like) rather than through hydrogen-bonding interactions (less ethanol-like).
TL;DR: A stereoselective synthetic method is developed for the preparation of multisubstituted 1,3-dienes via an allene–Claisen rearrangement of anti-allenyl alcohols, which is essential components of bongkrekic acid, in high stereoselectedivities.
Abstract: We herein developed a stereoselective synthetic method for the preparation of multisubstituted 1,3-dienes via an allene–Claisen rearrangement. The Claisen rearrangement of anti-allenyl alcohols provided (1E,3Z)-1,3-dienes, which are essential components of bongkrekic acid, in high stereoselectivities. To demonstrate the synthetic utility of the resulting 1,3-dienes, further functional transformations and Diels–Alder reactions are described.
TL;DR: In this paper, three distinct strategies for catalytic annulations between ynamides and 1-yn-3-ols are described; resulting carbo- and heterocycles were produced efficiently in one-pot operations using a gold catalyst.
Abstract: . Three distinct strategies for catalytic annulations between ynamides and 1-yn-3-ols are described; resulting carbo- and heterocycles were produced efficiently in one-pot operations using a gold catalyst. The chemoselectivities of these annulations are controlled by variations of the substituents of ynamides and 1-yn-3-ols. This reaction sequence involves initial alkoxylations of ynamides, followed by Claisen rearrangement of propargylic enol ethers, and ended with 6-endo-trig cyclizations of 1-allenyl-5-amide intermediates. Among these cascade annulations, the cyclizations of 5-allenyl-1-amides to yield 5,6-dihydro-2-pyranones and 6-alkylenecyclohex-2-ene-1-carboxamides are unprecedented in the literature.
TL;DR: Using quantum chemical simulations, this work investigated how the catalytic reaction mechanism is affected by electrostatic and hydrogen‐bond interactions, and identified a previously underappreciated water molecule, which separates the negative charges during the reaction.
TL;DR: Scandium-catalyzed asymmetric Claisen rearrangement reactions of 2-allyloxyindole and 2-propargyloxyindoles provide a novel approach to diverse 3-allyfiltration and 3-allenyloxindoles in excellent yields and enantioselectivity under mild reaction conditions.
Abstract: Scandium-catalyzed asymmetric Claisen rearrangement reactions of 2-allyloxyindoles and 2-propargyloxyindoles provide a novel approach to diverse 3-allyloxindoles and 3-allenyloxindoles in excellent yields (up to 99%) and enantioselectivity (up to 99% ee) under mild reaction conditions. The scandium catalyst was derived from Sc(OTf)3 and Pybox ligand.
TL;DR: In this paper, an efficient stereodivergent total synthesis of anti-Alzheimer agent (R)-(−) and (S)-(+)-arundic acid has been achieved from both chiral and nonchiral materials.
TL;DR: In this article, a one-pot procedure for the generation and Claisen rearrangement of benzyl vinyl ethers that contain an activating α-alkoxy substituent on the vinyl group was reported.
11 Aug 2017
TL;DR: In this article, a simple synthetic strategy to C2-symmetric bisannulated octacyclic novel cage diol was reported in eight linear steps starting with a readily available 1,4-hydroquinone.
Abstract: A simple synthetic strategy to C2-symmetric bisannulated octacyclic novel cage diol 20 is reported in eight linear steps starting with a readily available 1,4-hydroquinone 22. Here, an atom economic processes such as Claisen rearrangement, Diels-Alder reaction, intramolecular [2+2] photocycloaddition and ring-closing metathesis (RCM) were used as key steps. The synthetic approach demonstrated here opensup new opportunities to assembled highly functionalized complex cage molecules that are difficult to realize by conventional routes. The structure of the RCM product 19 was firmly established on the basis of single-crystal X-ray diffraction studies.